1. Field of the Invention
The present invention relates to methods of manufacturing products from silicone elastomers. More particularly, the present invention relates to an improved method of polishing silicone products in an alcohol or solvent solution and in the absence of any polishing abrasives to remove flashing or other sharp edges from the molded or stamped silicone or elastomer products.
2. General Background
Silicone materials such as silicone rubbers and silicone elastomers are used in the manufacture of a wide variety of products. These materials are particularly useful in biomedical applications because they are compatible with biological tissues and fluids, and are permeable to gases such as oxygen and carbon dioxide. Other desirable characteristics of silicone elastomer products include their flexibility, ease of molding, and relatively low cost.
Examples of such silicone elastomer products include soft contact lenses, intraocular lenses, medical catheters and cannulae, prosthetic implants, contraceptive devices, O-rings and other products in the automotive and other industries which require articles having a rounded, smooth, highly polished finish.
A highly polished finish, free of any sharp edges or surface irregularities, is required in biomedical applications. The silicone product is in direct contact with body tissues and the tearing or abrading of tissue by rough or non-smoothed surfaces could result in rupture of blood vessels, irritation or other trauma to the tissue.
It has been found that even minute irregularities can cause irritation of body tissues. This is a particularly serious problem with contact lenses and portions of intraocular lenses that contact the eye, where the tissue is extremely sensitive. The use of silicone materials for intraocular lenses is a relatively new development. Intraocular lenses formed of silicone are advantageous in that they can be folded and inserted through smaller incisions in the cornea than previously possible, resulting in fewer post-operative complications. Rough edges due to cutting of the lens blanks or flashing as the result of molding can cause intraocular irritation.
A satisfactory method of removing flashing from the edges of such lenses, and otherwise polishing them to obtain a smooth surface and enhanced optical clarity, was heretofore unknown. Such lenses are too small to trim by hand and polishing processes used for other types of lens materials such as polymethylmethacrylate are unsatisfactory.
In addition, soft contact lenses require a highly polished finish to prevent irritation of the interior of the eyelid and corneal epithelium. The eye is extremely sensitive to imperfections in contact lenses, and even slight ridges resulting from the molding process can produce irritation and discomfort. To this date, only expensive molding procedures or individual hand-grinding techniques have been available to produce the desired finish for these lenses.
Aside from intraocular lenses and contact lenses, other medical products manufactured from silicone elastomers and which require a highly polished finish include irrigation/aspiration cannula tip sleeves for use in phacoemulsification procedures. In this surgical procedure, ultrasonic energy is applied to break-up the natural lens of the eye. The cannula is inserted through a corneal incision to the vicinity of the lens and is used to aspirate or remove the lens fragments. During this procedure, the tip of the cannula often comes into contact with the sensitive eye tissue and therefore it must be devoid of sharp, rough, or irregular edges.
Mechanical devices utilizing smooth, frictionless movement also require highly polished, smooth surfaces of their silicone products. Obtaining such a highly polished, smoothly-finished silicone article is often difficult as these products are manufactured by curing molten silicone material in molds, wherein even the most precise dies result in some flashing and/or irregular edges. The products may be trimmed and polished, but these finishing procedures are generally done by hand, and are both time consuming and expensive, as well as imprecise, so that they do not result in the totally smooth or regular surface required. Further, many of these articles, particularly those for biomedical applications, are relatively small, and/or irregularly shaped, causing difficulties in obtaining the desired finish, and/or clarity.
The removal of imperfections from small and irregularly shaped silicone products is an unsolved problem in the art. It would be of great utility to provide a simple, economic, and effective method for polishing and/or clarifying silicone products for industrial, medical, and mechanical purposes.